1. Field of the Invention
The present invention relates to a technology which changes the communication speed in a communication apparatus which communicates with a peripheral apparatus.
2. Description of the Related Art
The technology which changes the communication speed in a communication apparatus which communicates with a peripheral device may include a system including a USB device and a host apparatus and being capable of performing communication via a USB (Universal Serial Bus) at two different communication speeds of a full speed and a high speed. The system changes the communication speed to/from a USB device to a lower full speed if a host apparatus detects deterioration of the communication quality during communication to/from the USB device at a high speed which is a higher speed than the communication speed. (Refer to Japanese Unexamined Patent Application Publication Nos. 2007-172160 and 2005-182380, for example).
Another technology has also been known that a host apparatus in such a system changes the communication speed to/from a USB device in accordance with the amount of data to be transferred to the USB device. In this case, if the amount of data is small, the communication speed is changed to a lower full speed. If the amount of data is large, the communication speed is changed to a high speed which is higher than the full speed. (Refer to Japanese Unexamined Patent Application Publication No. 2006-330831).
Another technology in a system which uses a USB for communication has been known in which a host apparatus dynamically changes the communication speed to/from a USB device without resetting the USB. (Refer to Japanese Unexamined Patent Application Publication No. 2007-172160).
In general, a high speed which is a higher communication speed produces large power consumption during data transfer and a standby state than a full speed which is a lower communication speed. However, switching the communication speed to the lower full speed only if deterioration in communication quality is detected or if a small amount of data is to be transferred may not sufficiently prevent the power consumption.
On the other hand, if the communication speed is always kept at the lower full speed, the power consumption can be suppressed, and deterioration in communication quality can be prevented, compared with the case where the communication speed is high. However, the communication speed may not be enough for applications which communicate with a USB device.